A nimble mongrel and his teenage owner have won Britain's Got Talent and helped ITV's flagship light entertainment show trounce its BBC rival in the ratings.

An average of 11.4 million viewers saw Ashleigh Butler and Pudsey triumph in BGT – more than twice as many as The Voice's 5.6 million.

ITV claimed the programme was the highest rating show of the year so far, nudging ahead of a Coronation Street episode that pulled in 11.2 million in January.

Adding viewers of ITV's +1 channel brought the audience to 11.9 million, and the peak audience to 14.5 million. The peak without +1 was 13.8 million.

The Voice was hampered by starting 50 minutes earlier than normal on Saturday. At one stage during a series of head-to-head clashes the BBC show won the ratings battle for three consecutive weeks, but since then it has been losing viewers.

Pudsey and 17-year-old Ashleigh took home BGT's £500,000 prize, leaving the favourites Jonathan and Charlotte in second place. Ashleigh trained her pet to jump, dance on his hind legs, meander through her legs and even run across the judges' table.

Pudsey, a border collie, bichon frise and Chinese crested cross, won over Simon Cowell, who said he had a soft spot for dogs. "I adore both you," he told them. "You have got better and better as the competition has progressed and to do what you did in such a short time is a miracle."

The Welsh boys choir Only Boys Aloud came in third with their rendition of Calon Lân.

Peter Fincham, ITV's director of television, said: "Britain's Got Talent 2012 has been an amazing series, with an incredibly high calibre of acts, culminating in a really special final. We are delighted that viewers tuned in in their millions to watch Ashleigh and Pudsey be crowned this year's winner."